diff --git a/src/evalfunc.c b/src/evalfunc.c
index 9e384da..b4e4220 100644
--- a/src/evalfunc.c
+++ b/src/evalfunc.c
@@ -7982,7 +7982,7 @@
 	return;
 
     if (argvars[1].v_type != VAR_UNKNOWN)
-	utf8 = (int)tv_get_number_chk(&argvars[1], NULL);
+	utf8 = (int)tv_get_bool_chk(&argvars[1], NULL);
 
     p = tv_get_string(&argvars[0]);